Predis

Tomaj\Hermes\Driver\PredisSetDriver is the same Redis layout as RedisSetDriver, with a Predis\Client and Predis method names. Use this class when you cannot load ext-redis. It is tested with Predis 2.3 and later and with Predis 3 (predis/predis: ^2.3 || ^3.0). Do not pass a Predis client to RedisSetDriver. The 4.0.0 split made those two types separate.

public function __construct(
    Client $redis,
    string $key = 'hermes',
    int $refreshInterval = 1,
    string $scheduleKey = 'hermes_schedule'
)

Emit and handle

This is examples/predis:

use Predis\Client;
use Tomaj\Hermes\Dispatcher;
use Tomaj\Hermes\Driver\PredisSetDriver;
use Tomaj\Hermes\Emitter;
use Tomaj\Hermes\Handler\EchoHandler;
use Tomaj\Hermes\Message;
use Tomaj\Hermes\Shutdown\PredisShutdown;

$redis = new Client([
    'scheme' => 'tcp',
    'host' => '127.0.0.1',
    'port' => 6379,
]);

$driver = new PredisSetDriver($redis);
$driver->setupPriorityQueue('hermes_low', Dispatcher::DEFAULT_PRIORITY - 10);
$driver->setupPriorityQueue('hermes_high', Dispatcher::DEFAULT_PRIORITY + 10);

$emitter = new Emitter($driver);
$emitter->emit(new Message('type1', ['message' => 1]), Dispatcher::DEFAULT_PRIORITY);

$driver = new PredisSetDriver($redis, 'hermes', 1);
$dispatcher = new Dispatcher($driver, null, new PredisShutdown($redis));
$dispatcher->registerHandler('type1', new EchoHandler());
$dispatcher->handle();

examples/predis/shutdown.php stops workers with:

new PredisShutdown($redis)->shutdown();

Commands

A due message, or a message with no executeAt, is sadd on the priority key. A future message is:

$this->redis->zadd($this->scheduleKey, [
    $this->serializer->serialize($message) => $message->getExecuteAt(),
]);

That member-to-score map is the shape Predis expects. It is the fix for issue #48, where a retry was scheduled with the arguments the other way around.

send() treats executeAt as "delay this" only when the value is truthy and greater than microtime(true). A null execute-at is not delayed.

Wait loop

zrangebyscore reads from -inf to the current time, passed as a string with microseconds (sprintf('%.6F', microtime(true))) because Predis 2 and 3 type the bound as int|string. It uses LIMIT OFFSET 0 COUNT 1. Each returned member is removed with zrem and passed back through send(). If it is still in the future it returns to the sorted set. If it is due, send() sadds it onto the default priority key, because send() is called with no priority argument.

The live queue is still a set. spop is not FIFO. Empty loops sleep $refreshInterval seconds when that value is not 0.

Priority order is the same as ext-redis: the highest number first. See Priority.

Shutdown checks use ShutdownTrait. Pair this driver with PredisShutdown, not RedisShutdown. PredisShutdown::shutdown() treats a Predis status payload of OK as success. shouldShutdown() treats a missing key (null from get) as "keep running".

FAQ

When should I choose Predis over ext-redis?

When you cannot install the phpredis extension. On 5.x also when you need delayed messages and retries, which only Predis promotes correctly there; from 6.0 RedisSetDriver promotes them too.

Is the Redis data layout the same?

Yes. Sets per priority and one sorted set for the schedule, so the key names and behaviour match RedisSetDriver.

Which Predis versions are supported?

Predis 2.3 and later, and Predis 3. The tests run against both the lowest (2.3.0) and the newest release. Predis 1.x and 2.0 to 2.2 emit PHP 8.4 deprecations and are no longer tested.

Which shutdown class goes with it?

PredisShutdown. RedisShutdown expects a phpredis Redis object.

Do priorities work the same way?

Yes. The highest number is polled first. 5.x used reverse registration order, issue #50. See Priority.

Is there a full Predis example?

Yes. All examples except the RabbitMQ recipe use Predis, starting with the welcome email tutorial.